Integrated system and method for methane production using off gas recycling to anaerobic digester from a gas separation membrane unit

A system for improved production of biogas from an anaerobic digester, comprising:

• an anaerobic digester comprising:
• i) a tank having a feedstock inlet and a biogas outlet, and
• ii) a recycle gas injector disposed within the tank adjacent to a bottom thereof, the anaerobic digester being adapted and configured to convert organic feedstock with a culture of anaerobic microbes into a product gas comprising methane and CO2;
• a feed gas conduit in downstream fluid communication with the anaerobic digester;
• a gas separation membrane unit comprising one or more gas separation modules each of which includes a plurality of gas separation membranes that are selective for CO2 over CH4 housed within a pressure vessel having a feed gas inlet in fluid communication with the feed gas conduit, a permeate gas outlet, and a retentate gas outlet, the gas separation membrane unit being adapted and configured to separate a stream of raw biogas obtained from the anaerobic digester into a methane enriched stream of biomethane and a CO2 enriched stream of permeate gas;
• a product gas conduit adapted and configured to receive the stream of biomethane from the gas separation membrane unit and feed the stream of biomethane towards a point of use;
• a recycle gas conduit in fluid communication between the permeate gas outlet and the recycle gas injector;
• and
• means for providing a driving force comprising a vacuum pump, blower, and/or biogas compressor that is adapted and configured to provide a pressure difference across the plurality of membranes serving as a driving force for the separation of the stream of raw biogas into the streams of biomethane and permeate gas.